Raj,
I think similar to the "interest graph", but Hunch (acq. EBay) referred to their product as building the "taste graph" -- quoting from the Wikipedia entry, "mapping every person to every entity -- and their affinity for that entity."
Perhaps another, more hypothetical, approach to graphs is the coming "internet of things" / connected devices -- i.e. devices that aren't just nodes with their own IP addresses but that are also reflections of their "owner" and thus somehow integrated into that person's relationships with other humans and their connected devices.

There is no doubt the social web has changed the way we use the internet and interact with each other. I believe a foundation of this "new web" is the social graph - which is sometimes referred to as the friend graph. Although Facebook may have won the "friend graph" (for now), other valuable...